Long-range guided-wave inspection is an effective method for rapidly surveying long structures for defects such as cracks and corrosion pits. Using this method, a short pulse of guided waves at a typical frequency of below 100 kHz is launched within a structure being tested. This incident pulse is reflected from a geometric irregularity in the structure. The reflected signals are detected in a pulse-echo mode.
This method of inspection is presently in practical use for inspection of piping networks in processing plants, and oil and gas transmission pipelines. When applied to piping, the guided wave technique can typically detect defects as small as 2-3% relative to the pipe wall cross sectional area, over a length of 30 meters on either side of a test probe position. In addition to detecting the presence or absence of defects, the defect signals resulting from long-range guided-wave inspection can be used to characterize defects. For example, defects can be characterized in terms of planar or volumetric, depth, axial extent, and circumferential extent.
In order to characterize defects from the defect signals, it is necessary to understand how defect signal waveforms relate to defect characteristics. When the waveform-defect characteristic relationship is established, algorithms relating these relationships may be developed. Modeling simulation of waveforms of defect signals from arbitrary-shaped defects is necessary for establishing relationships between the defect signal characteristics and the defect characteristics.
There are several known techniques for modeling guided-wave interaction with defects, such as finite element analysis, boundary element analysis, and related hybrid methods. Because these methods are tedious and computationally intensive, their use has been limited to two-dimensional modeling of guided wave interactions with simple geometry defects, such as a notch that is infinitely long in a plate or completely circumferential in a pipe. Presently, complex and expensive three-dimensional modeling is required to handle interactions with finite-sized and arbitrary-shaped defects and to simulate defect waveforms.